Automation for garage fan

I have elk security but have yet to dabble much with automation. I want to start by trying to solve this issue.

The garage gets hotter than the outside temperature. I think that the main heat source is from the car. There is an exhaust fan in the garage. Intake is from the small gaps around the garage doors.

Anyway, I would like to have this fan turn on and off based on the difference between the outside and inside temperature. Another solution (probably easier) is to turn the fan on early in the morning when outside air is cool.

I have messed with x10 a bit for turning the fan on and off. The signal was not reliable. Sometimes the fan would turn on and other times it would not. It may be a phase coupler issue but before going through the whole x10 signal troubleshooting, I thought I would get some opinions on a better solution. It seems that insteon two way communication would be more reliable than x10.

The fan is hardwired and controlled by a switch. I have played around with a smarthome switchlinc but have not been able to get reliable control. Usually an on command will turn the fan on but sometimes it will not. I have not done any troubleshooting. I hate to throw more money at this when there may be a better solution. Also, I thought that this may be a start of more automation projects and am not so sure x10 is the answer.

For automation there are a number of power line solutions or you can wire a relay or some such if you are comfortable working with line voltage and want to hard wire it.

As for the heat coming from the car... Are you saying you pull it in with the engine hot and that heats up the garage? Possible but garages are typically not insulated so they just tend to get hot. Mine is insulated and lags the outdoor temp - cooler than outside typically in the morning and warmer late in the day. I also want to automate a fan. But you need more than small cracks around the doors to get much airflow unless your doors fit very poorly. I haven't figured out a good solution but have considered a motor to open a window an inch or so.

The garage is well insulated (room above it) and on the north side of the house so the doors don't get much sun. I have been cracking a window as well for air intake and was thinking of installing some sort of vent. I would be interested to see what you come up with. The temperature difference between the garage and outside can be up to 15 degrees. Kind of nice in the winter but, if working there in the summer, it is hot.

For automation there are a number of power line solutions or you can wire a relay or some such if you are comfortable working with line voltage and want to hard wire it.

As for the heat coming from the car... Are you saying you pull it in with the engine hot and that heats up the garage? Possible but garages are typically not insulated so they just tend to get hot. Mine is insulated and lags the outdoor temp - cooler than outside typically in the morning and warmer late in the day. I also want to automate a fan. But you need more than small cracks around the doors to get much airflow unless your doors fit very poorly. I haven't figured out a good solution but have considered a motor to open a window an inch or so.

I'm pretty sure the cheapest way to do this is using a CAI Webcontrol. Buy two of the temp sensors for it and put one inside the garage and one outside. Use one of the TTL outputs and run that to a relay for on/off. (please note that cai output is only 20ma max). There are relays on ebay designed for hobby boards that run on 20ma or less and can control 10amp 120v loads.

The CAI has a programming interface which you can use to create your logic for when the fan should be on and when it should be off. You need to hook it to your LAN to program it, but once programmed it doesn't need internet connection. If you choose to keep it hooked to the internet, then you can manually control it from any internet connection (seems a bit unnecessary to me). Although, it does have 8 outputs, so you might want to run some lights or other things off of it and there may be value in having internet control of those things.

Total cost of this would be something like $60 and for that you would have several extra relays for whatever else you might want to hook up to it.

When you write your code for it, have it subtract inside temp from outside temp. If it is more than a number (like say 5), send it to one subroutine, less than some number (like -5) goes to a second sub routine. In the subroutine where it is more than 5(garage hotter), it can check the actual temp for being greater than some number (like say 80 degrees) and turn the fan on. If the temp drops below 80 or it is less than 5 degrees hotter inside vs outside, it will shut off.

On the flip side, you could use it to warm your garage in the winter. If the garage is colder than outside, and the garage is less than some temp (like maybe 50), you could have the fan draw some of the warmer outside air in.

Use a UPB switch to control the fan. You'll need a UPB relay switch to replace the regular switch, and a PIM to connect to your Elk. Total cost should run about $140.

But you still need to get the temp readings into Elk. That will cost about $120 more for two of them with shipping. Then you need to run wires from outside and from the garage to the temp sensors back to the Elk.

The CAI costs $40 with shipping, a relay board like this http://www.ebay.com/...=item336b1eff6e for $14, a 9v wall wart will power both the relays and the cai (hopefully you keep old ones sitting around for stuff like this), and two one-wire temp sensors for about $5 http://www.ebay.com/...=item3a66a960bd . Once the PLC code is written it is self contained, the cai is mounted right where the fan is located using the same power supply as the fan and the temp sensors can be run outside around the fan shroud and the other temp sensor stays inside somewhere close by. No need for any additional wiring.

That is how 99.99% of the world would do it. But that's not us! Plus it would just be an "on" above some temp and an "off" below some temp. There would be no accounting for temp difference inside to outside potentially resulting in the fan running when it is actually hotter outside than inside or when it is the same temp.